Structure of associates in tetramethylurea aqueous solutions from the data of Raman scattering spectroscopy

The results from investigating interactions between tetramethylurea (TMU) and water molecules by means of Raman light scattering spectroscopy (RS) are presented. It is established that spectroscopic manifestations of association of TMU and H(2)O molecules are observed for the TMU molecule valence vibration band nu(CO) 1638 cm(-1). By means of quantum-chemical calculations, it is shown that the band sensitivity to molecular environment is defined by the number of 5-6 H(2)O molecules. It is found that in a pure TMU medium, chain dimers are formed due to the interactions of molecular dipoles arranged in parallel and hydrogen bonds of the C-HaEuro broken vertical bar O type. Ground state geometries of TMU, TMU-TMU, H(2)O molecules and TMU center dot (H(2)O) (n) complexes (n = 1-14) are optimized by the density functional B3LYP procedure, using the 6-31++G(d, p) basis set. The main vibration frequencies are calculated in the harmonic approximation. Associate formation energies are calculated with allowance for the basis set superposition error (BSSE).